Polyamic Acid Resin and Polyamideimide Film

ABSTRACT

Provided are a polyamic acid resin derived from an aromatic diamine, an aromatic dianhydride, a cycloaliphatic dianhydride and an aromatic diacid dichloride, and a polyamideimide film including polyamideimide derived from an aromatic diamine, an aromatic dianhydride, a cycloaliphatic dianhydride and an aromatic diacid dichloride.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No.10-2017-0116249 filed Sep. 12, 2017, the disclosure of which is herebyincorporated in its entirety by reference.

TECHNICAL FIELD

The following disclosure relates to a polyamic acid resin and apolyamideimide film. More particularly, the following disclosure relatesto a polyamic acid resin derived from a combination of specificcomponents, and a polyamideimide film including polyamideimide derivedtherefrom, having adjusted optical properties and being capable ofimplementing a high modulus.

BACKGROUND

In general, polyimide has excellent mechanical and thermal properties,thereby being applied to various fields including an insulatingsubstrate field for forming circuits and devices. However, since acharge transfer complex is formed between aromatic rings at the time ofpolymerization to cause polyimide to be brown or yellow colored, leadingto low light transmittance in the visible light region, it is difficultto apply the polyimide to display materials.

As a method of improving the light transmittance of the polyimide tomake the polyimide colorless and transparent, a method of usingalicyclic diamine or aliphatic diamine as a diamine component to inhibitformation of an intramolecular charge transfer complex is known in theart. Japanese Patent Laid-Open Publication No. 2002-161136 (PatentDocument 1) discloses polyimide obtained by imidizing a polyimideprecursor formed by aromatic acid dianhydride such as pyromelliticdianhydride and trans-1,4-diaminocyclohexane, however, which representshigh transparency but has deteriorated mechanical physical properties.

As such, as a method for converting the yellow color of polyimide to becolorless and transparent, an attempt has been made to use variousfunctional monomers. However, since a polyimide film having a high lighttransmittance in the visible light region also has a high lighttransmittance value in a short wavelength region of 400 nm or less, whenthe film is exposed to ultraviolet rays, damage due to ultraviolet raysoccurred in a lower laminate structure of a display including thepolyimide film. In order to solve the problem, it was intended to use awidely used ultraviolet ray absorber or ultraviolet ray stabilizer,however, polyimide is processed at high temperature so that it is hardto use an additive, and even in the case of using the additive, a yellowindex was increased.

Thus, it is currently needed to develop a technology for polyimidehaving excellent inherent mechanical physical properties which is notdeteriorated by implementing a high modulus so that the polyimide may beapplied to various display material fields, and capable of preventingdamage of a lower laminate structure of a display including a polyimidefilm due to ultraviolet rays by decreasing a light transmittance in ashort wavelength region of 400 nm or less, so that the coverage may befurther broadened.

RELATED ART DOCUMENT Patent Document

-   (Patent Document 1) Japanese Patent Laid-Open Publication No.    2002-161136 (Jun. 4, 2002)

SUMMARY

An embodiment of the present invention is directed to providing apolyamic acid resin and a polyamideimide film which may have excellentmechanical physical properties simultaneously with a low yellow index,and have an excellent light transmittance in an entire wavelength regionof visible light and implement a low light transmittance in a shortwavelength region.

In particular, an embodiment of the present invention is directed toproviding a polyamideimide film capable of implementing a high modulus.

In addition, an embodiment of the present invention is directed toproviding a polyamideimide film capable of preventing ultravioletray-induced damage by ultraviolet ray exposure to a lower structure of adisplay including the polyamideimide film.

In one general aspect, a polyamideimide film includes polyamideimidederived from an aromatic diamine, an aromatic dianhydride, acycloaliphatic dianhydride and an aromatic diacid dichloride, wherein

the cycloaliphatic dianhydride includes a compound represented by thefollowing Chemical Formula 1, and

the polyamideimide film may have a total light transmittance of 88% ormore, and a light transmittance measured at 388 nm of 40% or less, asmeasured in accordance with the ASTM D1003 standard:

wherein

R₁ to R₄ are independently of one another, selected from the groupconsisting of hydrogen, halogen, a C₁ to C₁₀ alkyl group or a C₁ to C₁₀alkoxy group.

According to an exemplary embodiment of the present invention, thearomatic diamine may include 2,2′-bis(trifluoromethyl)-benzidine.

According to an exemplary embodiment of the present invention, thearomatic dianhydride may include 4,4′-hexafluoroisopropylidenediphthalic anhydride and biphenyltetracarboxylic dianhydride.

According to an exemplary embodiment of the present invention, thearomatic diacid dichloride may include terephthaloyl dichloride.

According to an exemplary embodiment of the present invention, a contentof the aromatic diacid dichloride may be more than 50 mol, based on 100mol of the aromatic diamine.

According to an exemplary embodiment of the present invention, a contentof the aromatic dianhydride may be 10 to 50 mol, based on 100 mol of thearomatic diamine.

According to an exemplary embodiment of the present invention, a contentof the aromatic dianhydride may be 5 to 25 mol of4,4′-hexafluoroisopropylidene diphthalic anhydride and 5 to 25 mol ofbiphenyltetracarboxylic dianhydride, based on 100 mol of the aromaticdiamine.

According to an exemplary embodiment of the present invention, a contentof the cycloaliphatic dianhydride may be 5 to 30 mol, based on 100 molof the aromatic diamine.

According to an exemplary embodiment of the present invention, thepolyamideimide film may have a modulus of 5.0 GPa or more, as measuredat an extension speed of 25 mm/min using UTM 3365 available fromInstron.

According to an exemplary embodiment of the present invention, thepolyamideimide film may have a yellow index of 3.0 or less, as measuredin accordance with the ASTM E313 standard.

According to an exemplary embodiment of the present invention, thepolyamideimide film may have a modulus of 5.0 GPa or more, as measuredat an extension speed of 25 mm/min using UTM 3365 available from Instronfor a specimen having a thickness of 55 μm, a length of 50 mm and awidth of 10 mm.

According to an exemplary embodiment of the present invention, thepolyamideimide film may have a total light transmittance of 88% or more,as measured in accordance with the ASTM D1003 standard, based on a filmhaving a thickness of 55 μm.

According to an exemplary embodiment of the present invention, thepolyamideimide film may have a yellow index of 3.0 or less, as measuredin accordance with the ASTM E313 standard, based on a film having athickness of 55 μm.

According to an exemplary embodiment of the present invention, thepolyamideimide film may have a light transmittance of 40% or less, asmeasured at 388 nm, based on a film having a thickness of 55 μm.

In another general aspect, an image display device includes thepolyamideimide film as described above.

In still another general aspect, a polyamic acid resin is derived froman aromatic diamine, an aromatic dianhydride, a cycloaliphaticdianhydride and an aromatic diacid dichloride, wherein

the cycloaliphatic dianhydride is represented by the following ChemicalFormula 1:

wherein

R₁ to R₄ are independently of one another, selected from the groupconsisting of hydrogen, halogen, a C₁ to C₁₀ alkyl group or a C₁ to C₁₀alkoxy group.

According to an exemplary embodiment of the present invention, thearomatic diamine may include 2,2′-bis(trifluoromethyl)-benzidine.

According to an exemplary embodiment of the present invention, thearomatic dianhydride may include 4,4′-hexafluoroisopropylidenediphthalic anhydride and biphenyltetracarboxylic dianhydride.

According to an exemplary embodiment of the present invention, thearomatic diacid dichloride may include terephthaloyl dichloride.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in more detail withreference to the exemplary embodiments and Examples including theaccompanying drawings. However, the following exemplary embodiments andExamples are only a reference for describing the present invention indetail, and the present invention is not limited thereto, and may beimplemented in various forms.

In addition, unless otherwise defined, all technical terms andscientific terms have the same meanings as those commonly understood bya person skilled in the art to which the present invention pertains, theterms used herein is only for effectively describing a certain exemplaryembodiment, and not intended to limit the present invention.

Throughout the present specification describing the present invention,unless explicitly described to the contrary, “comprising” any elementswill be understood to imply further inclusion of other elements ratherthan the exclusion of any other elements.

In addition, the singular form used in the specification and claimsappended thereto may be intended to also include a plural form, unlessotherwise indicated in the context.

In addition, “a polyamic acid solution”, which is a solution formed bymixing monomers in an organic solvent, refers to containing a polyamicacid resin obtained by copolymerization of monomers in the organicsolvent.

The inventors of the present invention provide a polyamideimide filmincluding an aromatic diamine, an aromatic dianhydride, a cycloaliphaticdianhydride and an aromatic diacid dichloride. That is, a modulus may besurprisingly excellent, a yellow index may be significantly lowered, anda light transmittance over an entire region of visible light may beraised, by deriving polyamideimide from a polyamic acid resin having acombination of specific aromatic diamine, dianhydride and aromaticdiacid dichloride. At the same time, it was found that a polyamideimidefilm preventing damage due to ultraviolet rays in a lower structure of adisplay including the polyamideimide film may be provided bysignificantly decreasing a light transmittance in a short wavelengthregion, thereby completing the present invention.

Specifically, in order to provide a resin and a film which may beapplied various display fields by improving optical properties as wellas mechanical and thermal properties, the present invention provides apolyamic acid resin including specific aromatic diamine, aromaticdianhydride, cycloaliphatic dianhydride and aromatic diacid dichloride,and a polyamideimide film derived therefrom.

According to an exemplary embodiment of the present invention, thepresent invention relates to a polyamideimide film includingpolyamideimide derived from an aromatic diamine, an aromaticdianhydride, a cycloaliphatic dianhydride and an aromatic diaciddichloride, wherein

the cycloaliphatic dianhydride includes a compound represented by thefollowing Chemical Formula 1, and

the polyamideimide film may have a total light transmittance of 88% ormore, and a light transmittance measured at 388 nm of 40% or less, asmeasured in accordance with the ASTM D1003 standard:

wherein

R₁ to R₄ are independently of one another, selected from the groupconsisting of hydrogen, halogen, a C₁ to C₁₀ alkyl group or a C₁ to C₁₀alkoxy group.

Preferably, according to an exemplary embodiment of the presentinvention, the present invention relates to a polyamideimide filmincluding polyamideimide derived from an aromatic diamine, an aromaticdianhydride, a cycloaliphatic dianhydride and an aromatic diaciddichloride, wherein

the aromatic diamine includes 2,2′-bis(trifluoromethyl)-benzidine,

the aromatic dianhydride may include 4,4′-hexafluoroisopropylidenediphthalic anhydride and biphenyltetracarboxylic dianhydride,

the cycloaliphatic dianhydride includes a compound represented by thefollowing Chemical Formula 1, and

the aromatic diacid dichloride includes terephthaloyl dichloride:

wherein

R₁ to R₄ are independently of one another, selected from the groupconsisting of hydrogen, halogen, a C₁ to C₁₀ alkyl group or a C₁ to C₁₀alkoxy group.

According to an exemplary embodiment of the present invention, thepolyamideimide film may have a total light transmittance of 88% or more,as measured in accordance with the ASTM D1003 standard. Preferably thetotal light transmittance may be 89% or more. Specifically, the totallight transmittance may be 88 to 99%. More preferably, the total lighttransmittance may be 89 to 95%. Here, the total light transmittance maybe measured, based on a specimen having a thickness of 55 μm.

In addition, according to an exemplary embodiment of the presentinvention, the polyamideimide film may have a light transmittance of 40%or less, as measured at 388 nm using UV-3600 available from Shimadzu.Preferably, the light transmittance measured at 388 nm may be 30% orless. Specifically, the light transmittance measured at 388 nm may be 1to 40%. Preferably, the light transmittance measured at 388 nm may be 5to 30%. Here, the light transmittance measured at 388 nm may bemeasured, based on a specimen having a thickness of 55 μm.

The polyamideimide film including the polyamideimide by the combinationof the present invention as described above has an excellent modulus,while significantly lowering a yellow index and raising a lighttransmittance over an entire wavelength region of visible light. At thesame time, as the light transmittance is significantly decreased in ashort wavelength region, damage due to ultraviolet rays in a lowerstructure of a display including the polyamideimide film may beprevented without an ultraviolet additive. In addition, since theultraviolet additive is not included, deterioration of physicalproperties of polyamideimide may be prevented, and thus, the film ispreferred.

According to an exemplary embodiment of the present invention, thecycloaliphatic dianhydride may include a compound represented by thefollowing Chemical Formula 1:

wherein

R₁ to R₄ may be independently of one another, selected from the groupconsisting of hydrogen, halogen, a C₁ to C₁₀ alkyl group or a C₁ to C₁₀alkoxy group.

Preferably, in Chemical Formula 1,

R₁ to R₄ may be independently of one another hydrogen or a C₁ to C₁₀alkyl group.

More preferably, in Chemical Formula 1,

R₁ to R₄ may be independently of one another hydrogen or a C₁ to C₅alkyl group.

Most preferably, specifically for example,1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) may be included.

When the cycloaliphatic dianhydride is included, a low yellow index maybe implemented, and a light transmittance in a visible light region maybe improved, in the polyamideimide film prepared by the combination ofthe aromatic diamine, the aromatic dianhydride and the aromatic diaciddichloride as described above, which is thus preferred.

According to an exemplary embodiment of the present invention, a contentof the cycloaliphatic dianhydride may be to 30 mol, based on 100 mol ofthe aromatic diamine. Preferably, the content may be 5 to 20 mol. Whenthe cycloaliphatic dianhydride is included at the content, a yellowindex is significantly decreased, and a light transmittance over anentire wavelength region of visible light may be raised, which is thuspreferred.

The aromatic diamine according to an exemplary embodiment of the presentinvention may include 2,2′-bis(trifluoromethyl)-benzidine. The aromaticdiamine may impart excellent optical properties by a charge transfereffect of fluorine substituents, and 2,2′-bis(trifluoromethyl)-benzidinemay provide polyamideimide which is an imidized product of a polyamicacid resin with a combination of an aromatic dianhydride, acycloaliphatic dianhydride and an aromatic diacid dichloride, therebyimplementing optical properties to be desired depending on a wavelengthregion, and also excellent mechanical physical properties.

Here, the aromatic diamine may be used by mixing2,2′-bis(trifluoromethyl)-benzidine and other known aromatic diaminecomponents, however, it is more preferred to use2,2′-bis(trifluoromethyl)-benzidine alone for implementing the effect tobe achieved.

The dianhydride according to an exemplary embodiment of the presentinvention includes an aromatic dianhydride and a cycloaliphaticdianhydride.

The aromatic dianhydride of the present invention is specifically forexample, any one or a mixture of two or more selected from the groupconsisting of 4,4′-hexafluoroisopropylidene diphthalic anhydride(6-FDA), biphenyltetracarboxylic dianhydride (BPDA),1,2,4,5-benzenetetracarboxylic dianhydride (PMDA),benzophenonetetracarboxylic dianhydride (BTDA), 4,4′-oxydiphthalicdianhydride (ODPA), bisdicarboxyphenoxy diphenylsulfide dianhydride(BDSDA), IBIS-BAN (CAS No. 867350-98-9), TBIS-MPN (CAS No. 933041-59-9)and the like. It is more preferred to use only4,4′-hexafluoroisopropylidene diphthalic anhydride andbiphenyltetracarboxylic dianhydride for implementing the physicalproperty effect to be desired.

A content of the aromatic dianhydride according to an exemplaryembodiment of the present invention may be 10 to 50 mol, based on 100mol of the aromatic diamine. Preferably, the content may be 10 to 40mol. More preferably, the content may be 20 to 40 mol.

More preferably, a content of the aromatic dianhydride according to anexemplary embodiment of the present invention may be 5 to 25 mol of4,4′-hexafluoroisopropylidene diphthalic anhydride and 5 to 25 mol ofbiphenyltetracarboxylic dianhydride, based on 100 mol of the aromaticdiamine. Preferably, the content may be 10 to 20 mol of4,4′-hexafluoroisopropylidene diphthalic anhydride and 10 to 25 mol ofbiphenyltetracarboxylic dianhydride. Within the range of the content,when the polyamideimide film is prepared, the light transmittance issignificantly decreased in a short wavelength region, and damage due toultraviolet rays in a lower structure of a display including thepolyamideimide film may be prevented, which is preferred.

According to an exemplary embodiment of the present invention, thearomatic diacid dichloride includes terephthaloyl dichloride for beingreacted with the aromatic diamine to form an amide structure in a highmolecular chain. Besides, other known aromatic diacid dichloride may befurther included. Specifically for example, any one or a mixture of twoor more selected from the group consisting of 1,4-naphthalenedicarboxylic dichloride, 2,6-naphthalene dicarboxylic dichloride,1,5-naphthalene dicarboxylic dichloride and the like may be used. It ispreferred to use terephthaloyl dichloride alone for adjusting opticalproperties depending on the range of the polyamideimide film, and alsosignificantly improving the modulus.

According to an exemplary embodiment of the present invention, a contentof the aromatic diacid dichloride may be more than 50 mol, based on 100mol of the aromatic diamine. Preferably, the content may be 55 mol ormore. Specifically, the content may be 55 to 90 mol, preferably 55 to 80mol, more preferably 55 to 75 mol.

When the content satisfies the range, the physical property balance tobe desired, that is, a high light transmittance over an entire region ofvisible light without deteriorating mechanical and thermal physicalproperties may be implemented, with the combination of other components.Besides, by implementing a low light transmittance even in a shortwavelength region of 400 nm or less, damage due to ultraviolet rays in alower structure of a display including the polyamideimide film may beprevented. In addition, a yellow index may be further decreased, and asynergistic effect of dramatically improving a modulus may beimplemented.

By copolymerizing a high content of the aromatic diacid dichloride asdescribed above, the polyamideimide film prepared therefrom hasdramatically improved optical properties, and at the same time mayimplement a high modulus, which are preferred.

In particular, there was difficulty in using the aromatic diaciddichloride at a high content more than 50 mol, based on the diamine dueto gelation and the like during a polymerization reaction. Thus,conventionally, in order to use the aromatic diacid dichloride at a highcontent, lithium chloride, calcium chloride or the like was usedtogether, however, these compounds leave a chloride ion to have a badinfluence on the environment or deteriorate the physical properties ofthe film. In order to solve the problems, in the present invention, acompositional ratio depending on a combination with other componentsincluding the aromatic diamine, the aromatic dianhydride and thecycloaliphatic dianhydride, and a reaction order and a polymerizationconcentration of the reaction components may be adjusted to dramaticallyincrease the content of the aromatic diacid dichloride, therebyachieving the physical property effect to be desired.

Since the specific example, content and the like of the above-describedaromatic diamine, aromatic dianhydride, cycloaliphatic dianhydride andaromatic diacid dichloride are described above, detailed descriptionwill be omitted.

In the present invention, the polyamic acid resin which is a precursorbefore preparing polyamideimide may be preferably a resin produced bycopolymerizing an aromatic diamine, an aromatic dianhydride, acycloaliphatic dianhydride and an aromatic diacid dichloride.

Specifically, a polyamic acid resin wherein the aromatic diamineincludes 2,2′-bis(trifluoromethyl)-benzidine, and the aromaticdianhydride includes 4,4′-hexafluoroisopropylidene diphthalic anhydrideand biphenyltetracarboxylic dianhydride, the cycloaliphatic dianhydrideincludes a compound represented by the following Chemical Formula 1, andthe aromatic diacid dichloride includes terephthaloyl dichloride, may beprovided.

wherein

R₁ to R₄ may be independently of one another, selected from the groupconsisting of hydrogen, halogen, a C₁ to C₁₀ alkyl group or a C₁ to C₁₀alkoxy group.

In the present invention, an equivalent ratio of the aromatic diamineand a mixture of the aromatic dianhydride, the cycloaliphaticdianhydride and the aromatic diacid dichloride is preferably 0.9:1 to1.1:1, and more preferably 1:1. When the range is satisfied, thephysical properties of the film including the film forming propertiesare improved when forming a film from polyamideimide which is obtainedby imidizing the polyamic acid resin derived from the monomer, which ismore preferred.

The polyamic acid resin may be provided as a polyamic acid solutiondissolved in a solvent, and the polyamic acid solution is a solution ofthe above-described monomers, and may include an organic solvent for asolution polymerization reaction. The kind of the organic solvent is notparticularly limited, and specifically for example, it is preferred touse any one or two or more selected from the group consisting ofdimethylacetamide (DMAc), N-methyl-pyrrolidone (NMP), dimethylformamide(DMF), dimethylformsulfoxide (DMSO), acetone, diethylacetamide, m-cresoland the like.

In the present invention, the polyamic acid solution including thepolyamic acid resin and the solvent may be imidized by further includingany one or two or more selected from the group consisting of animidization catalyst and a dehydrating agent, in addition to thepolyamic acid resin.

As the imidization catalyst, any one or more selected from the groupconsisting of pyridine, isoquinoline and β-quinoline may be used. Inaddition, as the dehydrating agent, any one or more selected from thegroup consisting of an acetic anhydride, a phthalic anhydride and amaleic anhydride may be used, but not necessarily limited thereto.

Any one or a mixture of two or more selected from the group consistingof the imidization catalyst and the dehydrating agent according to anexemplary embodiment of the present invention may be included at 1 to 5mol, based on 1 mol of the aromatic dianhydride and the cycloaliphaticdianhydride. Preferably, 1.5 to 3 mol may be included, but not limitedthereto.

In the present invention, the polyamic acid solution may be imidized toobtain the polyamideimide film. Here, imidization may be carried outusing a known imidization method. Chemical imidization is preferred.Chemical imidization of the polyamic acid solution by including pyridineand an acetic anhydride is more preferred.

The polyamic acid solution according to the present invention mayfurther include various forms of additives. As the additive, any one ortwo or more selected from the group consisting of a flame retardant, anadhesion improver, inorganic particle, an antioxidant, an ultravioletray inhibitor, a plasticizer, an antistatic agent and the like may befurther included, but not necessarily limited thereto.

In addition, the present invention provides an image display deviceincluding the above-described polyamideimide film.

The present invention provides a method for preparing a polyamideimidefilm including the following steps:

(a) dissolving an aromatic diamine in an organic solvent, then adding anaromatic dianhydride, a cycloaliphatic dianhydride and an aromaticdiacid dichloride thereto, and performing a reaction to prepare apolyamic acid solution;

(b) imidizing the polyamic acid solution to prepare polyamideimide; and

(c) coating a polyamide imide solution in which the polyamideimide isdissolved in an organic solvent.

In the present invention, the method for preparing a polyamideimide filmis not particularly limited, however, it is preferred to perform themethod using a reactor equipped with a stirrer, a nitrogen injectionapparatus, a dropping apparatus, a temperature controller and a cooler.

According to an exemplary embodiment of the present invention, step (a)of preparing a polyamic acid solution may be to add an organic solventin a reactor, dissolve an aromatic diamine therein, then react anaromatic dianhydride and a cycloaliphatic dianhydride, and then add anaromatic diacid dichloride to perform the reaction.

In addition, another exemplary embodiment of (a) preparing a polyamicacid solution may be to add an organic solvent to a reactor, dissolve anaromatic diamine therein, then perform a reaction with an aromaticdiacid dichloride, and then react an aromatic dianhydride and acycloaliphatic dianhydride. This is more preferred, since the content ofthe aromatic diacid dichloride in a finally obtained polymer may beincreased, that is, polymerization reaction uniformity is excellent inspite of a high solid content, and a high modulus may be implemented, inaddition to excellent optical properties.

According to an exemplary embodiment of the present invention, whenpreparing the polyamic acid solution, the reaction is performed byadding the aromatic diamine not altogether, but stepwisely to theorganic solvent, for increasing reactivity. In addition, it is preferredto firstly add the aromatic diamine to the organic solvent, and thensufficiently dissolve the aromatic diamine. Here, the organic solvent tobe used is as described above, and it is preferred to use dimethylacetamide or N-methyl-2-pyrrolidone. In addition, the content of theorganic solvent may be properly selected considering the molecularweight of polyamideimide which is a copolymerized product derived fromthe monomers, and may be 80 to 97 wt % in the entire composition. Thecontent is preferably 85 to 95 wt %, more preferably 87 to 95 wt %. Thatis, the solid content is 3 to 20 wt %, preferably 5 to 15 wt %, and morepreferably 5 to 13 wt %.

When the content of the organic solvent is less than 80 wt %, gelationmay occur during a polymerization process, a uniform solution may bedifficult to be obtained, a solution having a high viscosity out of anavailable range is formed, so that purification using the solvent maynot be easy. As such, when the purification is not done well, opticalproperties such as a light transmittance and a yellow index may bedeteriorated when forming a film. In addition, when the content of theorganic solvent is more than 97 wt %, solution formation is possible,but the yield of polyamideimide may be decreased.

Step (a) is performed under an inert gas atmosphere, specifically forexample, with nitrogen or argon gas refluxed in the reactor. Inaddition, a reaction temperature range is from room temperature to 80°C., specifically 20 to 80° C., and a reaction time is 30 minutes to 24hours, but not limited thereto.

Step (b) of imidization is to imidize the polyamic acid solutionprepared in step (a) to obtain polyamideimide, and a known imidizationmethod, for example, a thermal imidization method, a chemicalimidization method, and a combination of a thermal imidization methodand a chemical imidization method may be applied. It is preferred tosubject the solution to chemical imidization, but not limited thereto.

In addition, the imidization may be performed before or after coating apolyamideimide solution, and applied by the known various methods, andthus, is not limited.

In the present invention, the chemical imidization may be performed byfurther including any one or two or more selected from the groupconsisting of an imidization catalyst and a dehydrating agent in theprepared polyamic acid solution. It is preferred that the chemicalimidization is performed by adding any one or two or more selected fromthe group consisting of an imidization catalyst and a dehydrating agentto the polyamic acid solution prepared in step (a), in terms of thephysical properties of the obtained polyamideimide. More preferably, anyone or two or more selected from the group consisting of an imidizationcatalyst and a dehydrating agent are added to the polyamic acid solutionto perform imidization, and then purification using a solvent isperformed to obtain a solid content, which is dissolved in the solventto obtain the polyamideimide solution.

Here, as the dehydrating agent, any one or more selected from the groupconsisting of acetic anhydride, phthalic anhydride and maleic anhydridemay be used, and as the imidization catalyst, any one or more selectedfrom the group consisting of pyridine, isoquinoline and β-quinoline maybe used, but not limited thereto.

According to an exemplary embodiment of the present invention, it ispreferred to use a solvent which may significantly decrease thesolubility of the solid content of polyamideimide, specifically forexample, any one or more selected from the group consisting of water andalcohol, as the solvent used in the purification after imidizing thepolyamic acid solution.

When the solid content of polyamideimide is obtained by purification,and then dissolved in the organic solvent to obtain imidizedpolyamideimide, as the organic solvent to be used, a solvent identicalto or different from the organic solvent used when preparing thepolyamic acid solution may be used. Here, the content of the solvent maybe 70 to 95 wt %. The content is preferably 75 to 95 wt %, morepreferably 80 to 90 wt %.

In addition, when a viscosity of the polyamideimide solution prepared bydissolving the finally obtained polyamideimide in the solvent ismeasured, the viscosity may be 5,000 to 500,000 cps, preferably 8,000 to300,000 cps, more preferably 10,000 to 200,000 cps. Here, the viscosityis measured using a Brookfield viscometer at 25° C.

The polyamideimide obtained in the present invention has a weightaverage molecular weight of 50,000 to 1,000,000 g/mol, preferably 50,000to 800,000 g/mol, and more preferably 50,000 to 500,000 g/mol. Here, theweight average molecular weight is measured with polystyrene as astandard sample using 1260 Infinity available from Agilent Technologies,in which PL gel Olexis was used as a column, and 4 mg contained in 100ml of LiCl at 0.5 wt % with DMAc as a solvent was used as the sample. Inaddition, the polyamideimide may have a glass transition temperature of200 to 400° C., preferably 320 to 390° C.

Step (c) of coating a polyamideimide solution in which thepolyamideimide is dissolved in the solvent and subjecting the coatedsolution to heat treatment may be further included. The heat treatmentstep is to cast the polyamideimide solution on a substrate such as aglass substrate and subject the cast solution to heat treatment to forma film. Here, the term “polyamideimide solution’ described in step (c)refers to a coating composition for preparing a polyamideimide filmcontaining polyamideimide.

According to an exemplary embodiment of the present invention, it ispreferred that the heat treatment is stepwisely performed as an example.Preferably, the heat treatment may be stepwisely performed at 80 to 100°C. for 1 minute to 2 hours, at 100 to 200° C. for 1 minute to 2 hours,or at 250 to 300° C. for 1 minute to 2 hours. More preferably, thestepwise heat treatment depending on each temperature range is performedfor 30 minutes to 2 hours. Here, it is more preferred to perform thestepwise heat treatment by heating in a range of preferably 1 to 20°C./min when moving to each step. In addition, the heat treatment may beperformed in a separate vacuum oven, but not necessarily limitedthereto.

According to an exemplary embodiment of the present invention, thecoating may be performed using an applicator considering a thickness ofthe prepared film to form the film on the substrate, and the filmthickness may be 10 to 100 μm, preferably 20 to 90 μm, but not limitedthereto.

According to an exemplary embodiment of the present invention, thepolyamideimide film may have a modulus of 5.0 GPa or more, as measuredat an extension speed of 25 mm/min using UTM 3365 available fromInstron. Specifically, the modulus may be 5.0 to 10 GPa, preferably 5.0to 8.0 GPa. Here, the modulus may be measured, based on a specimenhaving a thickness of 55 μm, a length of 50 mm and a width of 10 mm.

In addition, according to an exemplary embodiment of the presentinvention, the polyamideimide film may have a total light transmittanceof 88% or more, as measured in accordance with the ASTM D1003 standard.Preferably the light transmittance may be 89% or more. Specifically, thetotal light transmittance may be 88 to 99%. Preferably, the total lighttransmittance may be 89 to 95%. Here, the total light transmittance maybe measured, based on a specimen having a thickness of 55 μm.

In addition, according to an exemplary embodiment of the presentinvention, the polyamideimide film may have a light transmittance of 40%or less, as measured at 388 nm using UV-3600 available from Shimadzu.Preferably, the light transmittance may be 30% or less. Specifically,the light transmittance measured at 388 nm may be 1 to 40%. Preferably,the light transmittance may be 5 to 30%. Here, the light transmittancemeasured at 388 nm may be measured, based on a specimen having athickness of 55 μm.

In addition, the polyamideimide film may have a yellow index of 3.00 orless, preferably 2.60 or less, as measured in accordance with the ASTME313 standard. Specifically, the yellow index may be 1.00 to 3.00,preferably 1.00 to 2.60. Here, the yellow index is measured using aColorQuest XE measuring device available from HunterLab. In addition,the yellow index may be measured, based on a specimen having a thicknessof 55 μm.

As described above, the polyamideimide film capable of implementingexcellent physical properties may be derived from the aromatic diamine,the aromatic dianhydride, the cycloaliphatic dianhydride and thearomatic diacid dichloride. Specifically, the film may be provided frompolyamideimide derived from the polyamic acid resin wherein the aromaticdiamine includes 2,2′-bis(trifluoromethyl)-benzidine, and the aromaticdianhydride includes 4,4′-hexafluoroisopropylidene diphthalic anhydrideand biphenyltetracarboxylic dianhydride, the cycloaliphatic dianhydrideincludes a compound represented by the following Chemical Formula 1, andthe aromatic diacid dichloride includes terephthaloyl dichloride.

wherein

R₁ to R₄ are independently of one another, selected from the groupconsisting of hydrogen, halogen, a C₁ to C₁₀ alkyl group or a C₁ to C₁₀alkoxy group.

The polyamideimide film prepared by the combination may implementoptical properties such as a high total light transmittance and a lowyellow index as described above, and also has an excellent modulus, andmay decrease a light transmittance in a short wavelength region.

The present invention may manufacture various forms of molded articlesusing the polyamideimide. As an example, the present invention may beapplied to a printed wiring board, a flexible circuit board and the likeincluding a film, a protective film or an insulating film, but notlimited thereto. Preferably, the present invention may be applied to aprotective film which may replace cover glass, and has a wideapplication range in various industrial fields including a display.

Hereinafter, the preferred Examples and Comparative Examples of thepresent invention will be described. However, the following Examples areonly a preferred exemplary embodiment, and the present invention is notlimited thereto.

The physical properties of the present invention were measured asfollows:

(1) Light Transmittance (Unit: %)

Total light transmittance of the films prepared in the Examples and theComparative Examples were measured using COH-400 available from NipponDenshoku in accordance with the ASTM D1003 standard. The lighttransmittance at 388 nm of the films prepared in the Examples and theComparative Examples were measured using UV-3600 available fromShimadzu.

(2) Yellow Index

The yellow index of the films prepared in the Examples and theComparative Examples was measured in accordance with the ASTM E313standard using ColorQuest XE (Mode type: Total transmission, Area view:0.375 in., UV filter: Nominal) available from HunterLab.

(3) Modulus

The modulus of the films having a length of 50 mm and a width of 10 mmprepared in the Examples and the Comparative Examples was measured usingUTM 3365 available from Instron, under the condition of pulling at 25mm/min at 25° C.

(4) Viscosity

The viscosity was measured using a Brookfield viscometer(Dv2TRV-cone&plate, CPA-52Z) at 25° C.

(5) Molecular Weight

The weight average molecular weight was measured using 1260 Infinityavailable from Agilent Technologies, with polystyrene as a standardsample, in which PL gel Olexis was used as the column, and 4 mgcontained in 100 ml of LiCl at a concentration of 0.5 wt % with DMAc asa solvent was used as the sample.

Example 1

Under a nitrogen atmosphere, methylene chloride and2,2′-bis(trifluoromethyl)-benzidine (TFMB) were added to a reactor andsufficiently stirred, and then terephthaloyl dichloride (TPC) was addedthereto and stirred for 6 hours to be dissolved and reacted. Thereafter,an excessive amount of methanol was used for precipitation andfiltration to obtain a reaction product, which was dried under vacuum at50° C. for 6 hours or more, and added again with DMAc to the reactorunder the nitrogen atmosphere, and 4,4′-hexafluoroisopropyllidenediphthalic anhydride (6FDA) was added thereto and sufficiently stirreduntil dissolved, and then biphenyltetracarboxylic dianhydride (BPDA) wasadded and stirred until dissolved, and then cyclobutanetetracarboxylicdianhydride (CBDA) was added and stirred until dissolved. Subsequently,pyridine and acetic anhydride were added to the solution at 2.5-foldmolar amount of the total added amount of dianhydrides, and stirred at60° C. for 1 hour. Here, the amount of each monomer was such that themole ratio of TFMB:BPDA:CBDA:6FDA:TPC was 100:10:20:15:55, and thesolution was adjusted to have a solid content of 12 wt %. The viscosityof the finally obtained polyamideimide was 33,000 cps, as measured usinga Brookfield viscometer at 25° C.

The obtained solution was solution-cast on a glass substrate using anapplicator. Thereafter, heat treatment was performed in a vacuum oven at100° C. for 30 minutes, at 200° C. for 30 minutes and at 300° C. for 30minutes, and then cooling was performed at room temperature, and thefilm formed on the glass substrate was separated from the substrate toobtain a polyamideimide film having a thickness of 55 μm. The result ofmeasuring the weight average molecular weight of the film was 205,000g/mol.

Example 2

A polyamideimide film having a thickness of 56 μm was prepared in thesame manner as in Example 1, except that the mole ratio ofTFMB:BPDA:CBDA:6FDA:TPC was 100:20:10:15:55. The weight averagemolecular weight of the prepared polyamideimide was 195,000 g/mol, andthe viscosity of the finally obtained polyamideimide was 27,000 cps, asmeasured using a Brookfield viscometer at 25° C.

Example 3

A polyamideimide film having a thickness of 56 μm was prepared in thesame manner as in Example 1, except that the mole ratio ofTFMB:BPDA:CBDA:6FDA:TPC was 100:10:5:15:70. The weight average molecularweight of the prepared polyamideimide was 210,000 g/mol, and theviscosity of the finally obtained polyamideimide was 30,000 cps, asmeasured using a Brookfield viscometer at 25° C.

Example 4

A polyamideimide film having a thickness of 55 μm was prepared in thesame manner as in Example 1, except that the mole ratio ofTFMB:BPDA:CBDA:6FDA:TPC was 100:15:10:15:60. The weight averagemolecular weight of the prepared polyamideimide was 190,000 g/mol, andthe viscosity of the finally obtained polyamideimide was 28,000 cps, asmeasured using a Brookfield viscometer at 25° C.

Example 5

A polyamideimide film having a thickness of 60 μm was prepared in thesame manner as in Example 1, except that biphenyltetracarboxylicdianhydride (BPDA) was not used, and the compound represented by thefollowing Chemical Formula 2 was further included, so that the moleratio of TFMB:TBIS-MPN:CBDA:6FDA:TPC was 100:5:25:15:55. The weightaverage molecular weight of the prepared polyamideimide was 195,000g/mol, and the viscosity of the finally obtained polyamideimide was28,000 cps, as measured using a Brookfield viscometer at 25° C.

Example 6

A polyamideimide film having a thickness of 58 μm was prepared in thesame manner as in Example 1, except that biphenyltetracarboxylicdianhydride (BPDA) was not used, and the compound represented by thefollowing Chemical Formula 3 was further included, so that the moleratio of TFMB:TBIS-BAN:CBDA:6FDA:TPC was 100:5:25:15:55. The weightaverage molecular weight of the prepared polyamideimide was 170,000g/mol, and the viscosity of the finally obtained polyamideimide was21,000 cps, as measured using a Brookfield viscometer at 25° C.

Example 7

A polyamideimide film having a thickness of 50 μm was prepared in thesame manner as in Example 1, except that biphenyltetracarboxylicdianhydride (BPDA) was not used, the mole ratio of TFMB:CBDA:6FDA:TPCwas 100:30:15:55, and 0.15 wt % of a UV additive (TBO,2,5-Bis(5-tert-butyl-2-benzoxazolyl)thiophene) was further included,based on the total amount of the composition. The weight averagemolecular weight of the prepared polyamideimide was 220,000 g/mol, andthe viscosity of the finally obtained polyamideimide was 58,000 cps, asmeasured using a Brookfield viscometer at 25° C.

Comparative Example 1

A polyamideimide film having a thickness of 50 μm was prepared in thesame manner as in Example 1, except that biphenyltetracarboxylicdianhydride (BPDA) was not used, and the mole ratio ofTFMB:CBDA:6FDA:TPC was 100:20:25:55. The weight average molecular weightof the prepared polyamideimide was 190,000 g/mol, and the viscosity ofthe finally obtained polyamideimide was 35,000 cps, as measured using aBrookfield viscometer at 25° C.

Comparative Example 2

A polyamideimide film having a thickness of 58 μm was prepared in thesame manner as in Example 1, except that cyclobutanetetracarboxylicdianhydride (CBDA) was not used, and the mole ratio ofTFMB:BPDA:6FDA:TPC was 100:20:25:55. The weight average molecular weightof the prepared polyamideimide was 180,000 g/mol, and the viscosity ofthe finally obtained polyamideimide was 32,000 cps, as measured using aBrookfield viscometer at 25° C.

Comparative Example 3

The process was performed in the same manner as in Example 1, exceptthat 4,4′-hexafluoroisopropylidene diphthalic anhydride (6FDA) was notused, and the mole ratio of TFMB:BPDA:CBDA:TPC was 100:20:20:60,however, the solution was hardened in a cloudy opaque state, so that theviscosity and the weight average molecular weight was not able to bemeasured.

Comparative Example 4

A polyamideimide film having a thickness of 55 μm was prepared in thesame manner as in Example 1, except that biphenyltetracarboxylicdianhydride (BPDA) and cyclobutanetetracarboxylic dianhydride (CBDA)were not used, and the mole ratio of TFMB:6FDA:TPC was 100:30:70. Theweight average molecular weight of the prepared polyamideimide was150,000 g/mol, and the viscosity of the finally obtained polyamideimidewas 15,000 cps, as measured using a Brookfield viscometer at 25° C.

Comparative Example 5

A polyamideimide film having a thickness of 59 μm was prepared in thesame manner as in Example 1, except that biphenyltetracarboxylicdianhydride (BPDA) was not used, and the compound represented by thefollowing Chemical Formula 4 was further included, so that the moleratio of TFMB:BPAF:CBDA:6FDA:TPC was 100:10:20:15:55. The weight averagemolecular weight of the prepared polyamideimide was 160,000 g/mol, andthe viscosity of the finally obtained polyamideimide was 18,000 cps, asmeasured using a Brookfield viscometer at 25° C.

Comparative Example 6

A polyamideimide film having a thickness of 52 μm was prepared in thesame manner as in Example 1, except that biphenyltetracarboxylicdianhydride (BPDA) was not used, and aromatic 3,4-oxydianiline (3,4-ODA)was included, so that the mole ratio of TFMB:3,4-ODA:CBDA:6FDA:TPC was90:10:30:15:55. The weight average molecular weight of the preparedpolyamideimide was 195,000 g/mol, and the viscosity of the finallyobtained polyamideimide was 30,000 cps, as measured using a Brookfieldviscometer at 25° C.

TABLE 1 Compositional ratio (mole ratio) TFMB 3,4-ODA BPDA BPAF TBIS-MPNTBIS-BAN CBDA 6FDA TPC Example 1 100 — 10 — — — 20 15 55 Example 2 100 —20 — — — 10 15 55 Example 3 100 — 10 — — —  5 15 70 Example 4 100 — 15 —— — 10 15 60 Example 5 100 — — — 5 — 25 15 55 Example 6 100 — — — — 5 2515 55 Example 7 100 — — — — — 30 15 55 Comparative 100 — — — — — 20 2555 Example 1 Comparative 100 — 20 — — — — 25 55 Example 2 Comparative100 — 20 — — — 20 — 60 Example 3 Comparative 100 — — — — — — 30 70Example 4 Comparative 100 — — 10 — — 20 15 55 Example 5 Comparative 9010 — — — — 30 15 55 Example 6 Light UV Total light transmittance Yellowadditive (wt %) Thickness (μm) transmittance (%) at 388 nm (%) indexModulus (GPa) Example 1 — 55 89.2 28.1 2.6 5.3 Example 2 — 56 89.0 11.82.9 5.1 Example 3 — 56 89.2 26.7 2.7 5.2 Example 4 — 55 89.0 17.5 2.55.0 Example 5 — 60 90.0 36.0 3.9 4.2 Example 6 — 58 89.5 1.5 14.4 4.3Example 7 0.15 50 89.7 12.0 4.3 5.2 Comparative — 50 89.8 69.5 2.4 4.8Example 1 Comparative — 58 89.2 11.3 3.6 4.5 Example 2 Comparative — — —— — — Example 3 Comparative — 55 90.0 70.2 3.2 4.5 Example 4 Comparative— 59 90.0 58.0 2.6 4.3 Example 5 Comparative — 52  83.93 0.7 18.7 4.8Example 6

As shown in Table 1, it was confirmed that the Examples according to thepresent invention had an excellent total light transmittance, a lowyellow index, and a high modulus. In particular, it was confirmed thatthe light transmittance measured at 388 nm was low. In particular,preferably, when the aromatic diamine includes2,2′-bis(trifluoromethyl)-benzidine, and the aromatic dianhydrideincludes 4,4′-hexafluoroisopropylidene diphthalic anhydride andbiphenyltetracarboxylic dianhydride, the cycloaliphatic dianhydrideincludes cyclobutanetetracarboxylic dianhydride (CBDA), and the aromaticdiacid dichloride includes terephthaloyl dichloride, all of theabove-described physical properties may be well-implemented.

However, Comparative Example 1 had a high light transmittance in a shortwavelength region which was measured at 388 nm, and a low modulus, ascompared with the Examples. In addition, Comparative Example 2 had ahigh yellow index, and Comparative Example 4 had a high lighttransmittance in a short wavelength region which was measured at 388 nm,and a low modulus, as compared with the Examples. In addition,Comparative Examples 5 and 6 had a high light transmittance in a shortwavelength region which was measured at 388 nm, or a very high yellowindex, and a low modulus, as compared with the Examples.

The polyamideimide film according to the present invention may haveexcellent mechanical physical properties, simultaneously with a lowyellow index and an excellent light transmittance in an entirewavelength region of visible light, and implement a low lighttransmittance in a short wavelength region.

In particular, as the polyamideimide film may implement a high modulus,and have a low light transmittance in a short wavelength region,ultraviolet ray-induced damage by ultraviolet ray exposure to a lowerstructure of a display including the polyamideimide film may beprevented, and thus, the polyamideimide film may be applied to variousdisplay fields.

Simultaneously, the polyamideimide film may significantly improve amodulus, and implement excellent mechanical strength, thereby beingapplied various fields including a display.

Hereinabove, although the present invention has been described by thespecific matters and specific exemplary embodiments, they have beenprovided only for assisting in the entire understanding of the presentinvention. Therefore, the present invention is not limited to theexemplary embodiments, and various modifications and changes may be madeby those skilled in the art to which the present invention pertains fromthis description.

Therefore, the spirit of the present invention should not be limited tothe above-described exemplary embodiments, and the following claims aswell as all modified equally or equivalently to the claims are intendedto fall within the scope and spirit of the invention.

What is claimed is:
 1. A polyamideimide film comprising polyamideimidederived from an aromatic diamine, an aromatic dianhydride, acycloaliphatic dianhydride and an aromatic diacid dichloride, whereinthe cycloaliphatic dianhydride includes a compound represented by thefollowing Chemical Formula 1, and the polyamideimide film has a totallight transmittance of 88% or more, and a light transmittance measuredat 388 nm of 40% or less:

wherein R₁ to R₄ are independently of one another, selected from thegroup consisting of hydrogen, halogen, a C₁ to C₁₀ alkyl group or a C₁to C₁₀ alkoxy group.
 2. The polyamideimide film of claim 1, wherein thearomatic diamine includes 2,2′-bis(trifluoromethyl)-benzidine.
 3. Thepolyamideimide film of claim 1, wherein the aromatic dianhydrideincludes 4,4′-hexafluoroisopropylidene diphthalic anhydride andbiphenyltetracarboxylic dianhydride.
 4. The polyamideimide film of claim1, wherein the aromatic diacid dichloride includes terephthaloyldichloride.
 5. The polyamideimide film of claim 1, wherein a content ofthe aromatic diacid dichloride is more than 50 mol, based on 100 mol ofthe aromatic diamine.
 6. The polyamideimide film of claim 1, wherein acontent of the aromatic dianhydride is 10 to 50 mol, based on 100 mol ofthe aromatic diamine.
 7. The polyamideimide film of claim 3, wherein acontent of the aromatic dianhydride is 5 to 25 mol of4,4′-hexafluoroisopropylidene diphthalic anhydride and 5 to 25 mol ofbiphenyltetracarboxylic dianhydride, based on 100 mol of the aromaticdiamine.
 8. The polyamideimide film of claim 1, wherein a content of thecycloaliphatic dianhydride is 5 to 30 mol, based on 100 mol of thearomatic diamine.
 9. The polyamideimide film of claim 1, wherein thepolyamideimide film has a modulus of 5.0 GPa or more, as measured at anextension speed of 25 mm/min using UTM 3365 available from Instron. 10.The polyamideimide film of claim 1, wherein the polyamideimide film hasa yellow index of 3.0 or less, as measured in accordance with the ASTME313 standard.
 11. The polyamideimide film of claim 9, wherein thepolyamideimide film has a modulus of 5.0 GPa or more, as measured at anextension speed of 25 mm/min using UTM 3365 available from Instron, fora specimen having a thickness of 55 μm, a length of 50 mm and a width of10 mm.
 12. The polyamideimide film of claim 1, wherein thepolyamideimide film has a total light transmittance of 88% or more,based on a thickness of 55 μm.
 13. The polyamideimide film of claim 10,wherein the polyamideimide film has a yellow index of 3.0 or less, asmeasured in accordance with the ASTM E313 standard, based on a thicknessof 55 μm.
 14. The polyamideimide film of claim 1, wherein thepolyamideimide film has a light transmittance measured at 388 nm of 40%or less, based on a thickness of 55 μm.
 15. An image display devicecomprising the polyamideimide film of claim
 1. 16. A polyamic acid resinderived from an aromatic diamine, an aromatic dianhydride, acycloaliphatic dianhydride and an aromatic diacid dichloride, whereinthe cycloaliphatic dianhydride includes a compound represented by thefollowing Chemical Formula 1:

wherein R₁ to R₄ are independently of one another, selected from thegroup consisting of hydrogen, halogen, a C₁ to C₁₀ alkyl group or a C₁to C₁₀ alkoxy group.
 17. The polyamic acid resin of claim 16, whereinthe aromatic diamine includes 2,2′-bis(trifluoromethyl)-benzidine. 18.The polyamic acid resin of claim 16, wherein the aromatic dianhydrideincludes 4,4′-hexafluoroisopropylidene diphthalic anhydride andbiphenyltetracarboxylic dianhydride.
 19. The polyamic acid resin ofclaim 16, wherein the aromatic diacid dichloride includes terephthaloyldichloride.